Respiration is a fundamental biological process involving the exchange of gases between an organism and its environment. Terrestrial vertebrates, including reptiles, rely on breathing air for this process. Unlike some aquatic organisms that can absorb oxygen from water, reptiles depend almost entirely on a specialized internal organ system to facilitate gas exchange.
Reptile Lungs
The primary respiratory organs in reptiles are their lungs. These sac-like structures vary in internal complexity among species. Compared to mammalian lungs, which feature extensive branching into numerous tiny air sacs called alveoli, reptile lungs generally exhibit a simpler structure. However, many reptile lungs still contain small pockets, or faveoli, that increase the surface area available for gas exchange.
Reptile lungs are categorized by internal partitioning. Some species possess unicameral lungs, which are single-chambered, while others have multicameral lungs, characterized by multiple chambers or subdivisions. This variation in lung structure reflects the diverse physiological demands and lifestyles across different reptile groups. Despite these structural differences, all reptile lungs draw air in and transfer oxygen to the bloodstream.
The Mechanics of Respiration
Reptiles primarily move air in and out of their lungs through a process called aspiration breathing, where air is pulled into the lungs by negative pressure. Most reptiles, unlike mammals, do not possess a muscular diaphragm to assist with breathing. Instead, they largely rely on the contraction and relaxation of intercostal muscles, which are located between their ribs.
These muscles expand and contract the rib cage, altering the volume of the body cavity and creating pressure changes that draw air into the lungs during inspiration and push it out during expiration. The glottis, a small opening behind the tongue, plays a role in controlling airflow by opening during inhalation and exhalation.
Diverse Breathing Strategies
Reptile respiration showcases a range of specialized adaptations reflecting their varied forms and habitats. Snakes, with their elongated bodies, often have one functional lung, typically the right one, while the left lung may be reduced or absent. During the process of swallowing large prey, which can take an extended period, snakes can extend their glottis out the side of their mouth, allowing them to continue breathing.
Turtles and tortoises face a unique challenge due to their rigid shells, which prevent the expansion and contraction of their rib cage. To overcome this, they employ specialized muscles connected to their limbs or internal organs to change the internal volume of their body cavity for breathing. Some aquatic turtles can even perform cloacal respiration, absorbing oxygen from water through highly vascularized sacs located in their cloaca, which is a multipurpose opening.
Crocodilians, including alligators and crocodiles, possess a unique “hepatic piston” mechanism. This involves a muscle attached to their liver and pelvis that pulls the liver backward, creating a negative pressure that expands the lungs and draws in air. This specialized system allows them to efficiently ventilate their lungs, even while submerged. Lizards generally use rib movements for breathing, though some may exhibit variations based on their body shape or engage in “buccal pumping” by moving the floor of their mouth to force air into the lungs.